Actuator Guide - Norgren Pneumatics. Motion Control Equipment ...

INTRODUCTION
Pneumatic actuators, of which cylinders are the most common,
are the devices providing power and movement to automated
systems, machines and processes. A pneumatic cylinder is a
simple, low cost, easy to install device that is ideal for
producing powerful linear movement over a wide range of
velocities, and can be stalled without causing internal damage.
Adverse conditions can be easily tolerated such as high
humidity, dry and dusty environments and repetitive
cleandown with high pressure hoses.
The diameter or bore of a cylinder determines the maximum
force that it can exert and the stroke determines the maximum
linear movement that it can produce. Cylinders are designed to
work at different maximum pressures up to 16 bar. The
pressure actually supplied to a cylinder will normally be
reduced through a pressure regulator to control the thrust to a
suitable level. As an example of cylinder power, a 40mm bore
cylinder working at 6 bar could easily lift an 80kg man.
The basic construction of a typical double acting single rod
cylinder is shown in the cut away section (Figure 1), where the
component parts can be identified.
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Figure 1: Main components of a cylinder
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Key:
1 Cushion seal 8 Front port
2 Magnet 9 Magnetically operated switch
3 Cushion sleeve 10 Piston rod
4 Barrel 11 Wear ring
5 Nose bearing 12 Piston seal
6 Rod seal and wiper 13 Rear end cover
7 Front end cover 14 Cushion adjustment screw
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Pneumatic actuators are made in a wide variety of sizes, styles
and types including those giving a semi rotary output. Each
major type will be covered in concept.
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FUNDAMENTAL DESIGNS
SINGLE ACTING CYLINDERS
Single acting cylinders use compressed air for a power stroke
in one direction only. The return stroke is effected by a
mechanical spring located inside the cylinder. For single
acting cylinders with no spring, some external force acting on
the piston rod causes its return. Most applications require a
single acting cylinder with the spring pushing the piston and
rod to the instroked position. For other applications sprung
outstroked versions can be selected. Figure 2 shows both
types of single acting cylinder.
Figure 2: Single acting cylinder
The spring in a single acting cylinder is designed to provide
sufficient force to return the piston and rod only. This allows
for the optimum efficiency from the available air pressure.
Most single acting cylinders are in the small bore and light duty
model ranges and are available in a fixed range of stroke sizes.
It is not practical to have long stroke or large bore single acting
cylinders because of the size and cost of the springs needed.
Single acting cylinders with no spring have the full thrust or
pull available for performing work. These are often double
acting cylinders fitted with a breather filter in the port open to
atmosphere. The cylinder can be arranged to have a powered
outstroke or a powered instroke (Figure 3).
Figure 3. Single acting cylinder with no spring, push and pull